Mr. Rumsfeld says he does not know if the terrorist leader is alive or dead or whether the new audio-tape really contains his voice.

But speaking in a nationwide radio call-in show Thursday on Infinity Broadcasting, Mr. Rumsfeld voices his doubts.

"I suspect if he were alive and healthy, he would be doing video-tapes, which seems to be his preference," he said. "I'm told in this instance, he very likely called in, somebody called in, and gave those words over a telephone of some sort so a tape does not exist that was an original tape."

Osama bin Laden has not been seen since late last year at the height of the U.S. bombing campaign against terrorist targets in Afghanistan.

Mr. Rumsfeld says it would be interesting to know if the tape, which hails recent terrorist attacks, really does contain bin Laden's voice because then people would know if he really is still alive.

But he says it does not really make a difference. He says U.S. officials remain alert and are continuing to try and put pressure on al-Qaida worldwide.

In the wide-ranging radio call-in show, Mr. Rumsfeld handled an array of questions dealing with a possible new conflict with Iraq, including the likely length of a war. He says he cannot predict how long it might last but he says it will definitely not spin out of control into a global war.

"I can't tell you if the use of force in Iraq today would last five days, five weeks or five months. But it certainly is not going to last any longer than that and it won't be a World War III," he said.

Mr. Rumsfeld also says U.S. forces today are vastly more powerful than those who fought in the 1991 Gulf war. And he says Iraq's military capabilities have declined substantially in the intervening years.

Earlier in the day, Mr. Rumsfeld said there is no doubt that Iraq has weapons of mass destruction, no matter what its officials might be saying.

Mr. Rumsfeld also said the purpose of the latest U.N. Security Council resolution is to get international inspectors into Iraq to make their own conclusions about Baghdad's weapons programs.

Mr. Rumsfeld made those comment during a brief appearance before reporters with Kazakhstan's visiting Defense Minister.